James Thomas Johnston (January 19, 1839 – July 19, 1904) was an American lawyer, Civil War veteran, and politician who served two terms as a U.S. Representative from Indiana from 1885 to 1889.

During the Civil War he enlisted as a private in Company C, Sixth Indiana Cavalry, in July 1862.

He transferred to Company A, Eighth Tennessee Cavalry, in September 1863 and was commissioned as a second lieutenant, serving until January 1864, when he resigned.

Commissioned as a lieutenant and assistant quartermaster of the One Hundred and Forty-ninth Regiment, Indiana Volunteer Infantry, he was mustered out in September 1865.

This article incorporates public domain material from the Biographical Directory of the United States Congress